Hi everyone. I have a betta fish who I've had for about 11 months. When I first got him I was very misinformed by the pet shop and had him in a tiny bowl.

He one day turned brown and I figured out it was from being too cold so I got him a nice large tank with a few plants and 2 apple snails. I got this tank a few weeks ago and he's been great. Blowing bubbles, eating and very active.

But last night I suddenly noticed he had a white patch by his side fin and he wasn't using that fin any more. Now it has turned black/brown and the fin looks ripped. I'm not sure if it is velvet or body rot or something else. Please help!

My parents bought the tank and put him in it while I was away and I'm not sure if they added any rock salt. I changed water and added some now, do you think this will help?

Welcome. How big is his new tank & are your running a filter on it? How often have you been doing water changes? How big are the water changes? Are you using a water conditioner, which one? Have you tested the water for ammonia, nitrites & nitrates? Aq salt can be useful for some things but harmful if used for too long.